1. Field of the Invention
The present invention relates to a low-fat food and a taste-improving agent that can be used to impart fat-like richness and smoothness to the taste of a low-fat food.
2. Brief Description of the Related Art
In recent years, attention has been focused on problems associated with lifestyle-related diseases due to excess intake of calories and fat. As a result, in the food industry, there is increasing interest in low-calorie, low-fat, non-fat foods, or the like because of diversified consumer needs and growing health consciousness. On the basis of those demands, products have been developed in various fields. However, because fat contributes greatly to food palatability, the general taste of low-fat or non-fat foods is plain or bland, is weak in kokumi, and also is weak in fat-derived richness and smoothness. Therefore, low-fat or non-fat foods are not always appealing to the consumer. In the present circumstances, consumer preferences are not sufficiently satisfied.
Furthermore, in the field of dairy products, in particular, although there are many product groups in which milk fat is replaced with vegetable oil or the like, the difference in the taste is clear in many cases.
Thus far, various efforts have been implemented in order to solve the above-mentioned problems. In relation to dairy products, the following are examples of attempts to improve the taste of low-fat products: incorporating a water-soluble dietary fiber (JP 2006-158232 A); using a chemically-modified starch, or the like, in combination with a water-soluble dietary fiber (JP 2004-215563 A and JP 2004-267160 A); and using agar (JP 2006-180792 A). Furthermore, various technologies have been tried to replace fat, such as an oil and fat composition focused on the constituent fatty acids (JP 2002-138296 A).
However, in all of the above cases, consumer demands have not been sufficiently satisfied. These products and methods fail in one or more aspects of palatability, such as fragrance, flavor, taste, or texture, and in terms of too many production steps and prices as well.
The calcium receptor (also called Calcium Sensing Receptor (CaSR)) has 1,078 amino acids, and is classified into class C of the seven-transmembrane receptors (G protein-coupled receptor, or GPCR). Cloning of the gene for the calcium receptor was reported in 1993 (Nature, 1993, Vol. 366(6455), pp. 575-580), and the calcium receptor is known to cause various cell responses via elevation of the intracellular calcium levels, etc., when activated by calcium, etc. The nucleotide sequence of the human calcium receptor is registered with GenBank under Accession No. NM—000388, and is well conserved among animals.
The calcium receptor may act to promote or suppress biological functions. Therefore, at present, therapeutic agents that either activate or inhibit the calcium receptor are appropriately used in the treatment of diseases of the neurological, hepatic, cardiovascular, and digestive systems, and other diseases, depending on the pathological conditions. For example, the calcium receptor is able to detect increased blood calcium in the parathyroid, and then suppress the secretion of the parathyroid hormone (PTH) to correct the blood calcium level. Therefore, reduction of the blood calcium level is expected for a calcium receptor activator. It has been actually reported that when a calcium receptor activator is used to treat secondary hyperparathyroidism in a hemodialysis patient, it reduces the PTH level without elevating the calcium and phosphorus levels.
Since a functional analysis of the calcium receptor has been conducted mainly for calcium homeostasis, the applications, therefore, have so far mainly focused on bone metabolic diseases in which calcium regulation is involved. However, it has become clear that the calcium receptor is widely distributed in living bodies other than the parathyroid and kidney from the results of genetic expression analyses etc. (J. Endocrinol., 2000, Vol. 165(2), pp. 173-177 and Eur. J. Pharmacol., 2002, Vol. 447(2-3), pp. 271-278), and the possibility that the calcium receptor is involved in various biological functions and perhaps even the cause of some diseases has been proposed. For example, there has been speculation that the calcium receptor is involved in the functions of the liver, heart, lung, gastrointestinal tract, lymphocytes, and pancreas. It has also been confirmed that the calcium receptor is expressed in a wide range of tissues by analyzing RNAs extracted from rat tissue using RT-PCR. Therefore, the potential applications for activators and inhibitors of the calcium receptor are rapidly increasing.
Moreover, in addition to calcium, cations such as a gadolinium cation, basic peptides such as polyarginine, polyamines such as spermine, amino acids such as phenylalanine, and so forth have been reported as calcium receptor activators (Cell Calcium, 2004, Vol. 35(3), pp. 209-216). It has also been reported, that glutathione (γ-Glu-Cys-Gly), a low molecular weight peptide, is a CaSR activator, but there is no mention or suggestion that the CaSR is involved in any function of taste (J. Biol. Chem., 2006, Vol. 281(13), pp. 8864-8870.
Thus far, it has not been reported that an amino acid or a peptide having a particular structure is useful as a calcium receptor activator. In addition, it has not been previously reported that an amino acid or a peptide which is able to activate a calcium receptor can impart fat-like richness and smoothness to the taste of a low-fat food.